August 21, Deepwater MPD / PMCD

Transcription

1 August 21, 2011 Deepwater MPD / PMCD

2 Managed Pressure Drilling (MPD) Pressure held on top of riser while drilling. Drill in overbalance condition Pressurized Mud Cap Drilling (PMCD) Pressure of mud column in riser and wellbore plus surface maintained pressure should equal formation pressure at top of carbonates. Drill in at balance condition

3 MPD Objectives - GSF Explorer Prevent gas entering riser. Improved riser degassing capabilities. Early kick and loss detection and automated reaction to these events. Allows Pressurized Mud Cap Drilling (PMCD) to be conducted safely. Ability to quickly manipulate the pressures (up or down) within the wellbore without the need for mud weight up and circulation.

4 Plan to drill in MPD mode for kick detection for drilling hole section above carbonates. Drill overbalanced with RCD bearing installed and maintain surface applied pressure on the well. Pressure on welll maintained by circulating through secure manifold choke. Improved kick detection

5 MPD - PMCD Switch Application MPD to be used in overbalance mode until the losses in the carbonates become excessive thereafter the system will be changed over to a PMCD (pressurized mud cap drilling) arrangement. Will use PMCD while drilling carbonates while experiencing severe fluid losses Avoid floating mud cap drilling Accurate determination of formation pressures Maintain well fluid level at surface

6 GSF Explorer MPD Equipment Requirements Rotating Control Device (RCD) 21 ¼ 2k Riser Annular BOP Riser Flow Spool Drilling Choke Manifold (Secure) Buffer Manifold Two Phase Separator Coriolis flow meter Drill String Floats - Plunger Type (connections stripping in/out)

7 Approx meters of riser between flow spool and BOP

8 General Arrangement MPD Configuration

9 Secure Manifold Two Phase Separator

10 Inline Coriolis Flow Meter

11 Sequential Operations MPD to PMCD Start MPD operations with overbalanced fluid RCD Kill line filled with base oil prior to drilling ahead Drill ahead MPD mode encounter carbonates with acceptable losses Take significant losses in carbonates Close Annular BOP Determine reservoir pressure = fracture pressure of carbonates using kill line Pressure mud column below BOP plus kill line hydrostatic Lighten riser fluid till it is just < top fracture pressure Continue drilling down drill string in PMCD mode with seawater Pump down annulus periodically to keep it gas free (bullhead to the top fracture) Kill Line Annular Choke Line

12 MPD Operations GSF Explorer Ability to stay within a narrow drilling windows (Pore vs. Frac.). Mitigate against losses:- early warning and ability to react quickly by decreasing back pressure. Safe means to drill section :- Increased kick detection sensitivity and reaction. Back pressure can be used to quickly supplement drilling fluid density when required if an influx is detected With MPD maintain CBHP

13 PMCD Operations GSF Explorer Annulus mud weight/press < pore pressure. Annulus fluid level at surface casing pressure. Pressure monitored at MPD manifold. Pump down drill string with seawater. Pump down riser boost with original weight mud SBM will minimize gas migration as it goes into solution.

14 Constant Bottom Hole Pressure - Example Make a Connection riser Boost Pump ON Static Mud Weight 11.5 ppg Pumps On Annular Friction Loss 0.25 ppg Stop Pumps Stop RPM RPM Friction Increase 0.09 ppg Surface Back Pressure 0.41 ppg Drilling Window PORE PRESSURE 11.5 ppg Bottom hole Pressure Stays The Same ppg FRACTURE PRESSURE 12.4 ppg

15 MPD & PMCD Carbonate Section Drill below the 11-7/8 shoe prior to entering the carbonate section. To be drilled in MPD Mode. Carbonates are anticipated to be vugular and/or fractured and may lead to severe/total losses with no returns. Depending on the loss rate > 20% PMCD will commence. There may be further losses as the pore pressure decreases (in PMCD mode) as the carbonates are drilled deeper.

16 Kill line Pressure Riser Boost Line Kill line prefilled with treated base fluid Choke Line Kill Line Kill line pressure to balance pore pressure in carbonates Silt/Sand Carbonate section below 11 7/8 shoe 4300m brt Shale Drilling in MPD mode Potential for gas in Carbonate section in the Fractures & Vugs Carbonate Sand / Shale /Coal MPD Drilling into Carbonates losses> 20% Close in (annular BOP) open kill line to base oil and record pressure

17 Light mud to Riser annulus via boost Kill Line Pressure Annulus Pressure at MPD Choke Riser Boost Line Riser Boost Line Choke Line Kill Line Choke Line Kill Line Silt/Sand Silt/Sand 4300m brt 4300m brt Shale Shale Carbonate Carbonate Sand / Shale /Coal Sand / Shale /Coal Calculate lighter mud in riser to give +/ psi surface annular back pressure displace into well Pump seawater down string establish stable injectivity at drilling rate

18 Annulus Pressure at MPD Choke Monitor Surface annular pressure Lighter Riser mud stays in the riser annulus Drop in surface annular pressure Riser Boost Line Choke Line Kill Line Silt/Sand Periodic pumping to annulus maintains it hydrocarbon free pump in at BOP 4300m brt Shale New loss zone at lower pressure Possibility of X flow between loss zones Seawater carries cuttings into loss zone Sand / Shale /Coal Carbonate Drill ahead w/seawater down string, Bullhead +/- 20bbls original weight mud down riser boost annulus every hour. Drill ahead w/ seawater, further loss zone encountered. Shut in and assess pressures using kill line.

19 PMCD During PMCD the pore pressure may start to decrease this will be noticed by a drop in surface annular pressure. Shut in well on upper BOP annular & open annulus again to base fluid in the kill line & recalculate new pore pressure. Evaluate whether to change out the riser to lighter mud or to pump more lighter mud below BOP.

20 Indications an increase in Pump pressure and annular pressure Control Options Depending on pressures involved: Increase pressure to induce losses Revert to MPD drilling Cuttings plugging off the loss zone/s Drill ahead PCWD Cuttings plugging off loss zone. Pressure increase in annulus & DP

21 PMCD Should the pump pressure and the surface annular pressure rise together, this is indicative of the loss zone starting to heal over. Depending on the pressures seen. Induce further fractures and continue in PMCD mode Return to MPD mode.

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